Commutating device for dynamo-electric machines.



M. WALKER. COMMUTATING DEVICE FOR DYNAMO ELECTRIC MACHINES.

APPLICATION FlLED NOV 30, I910. 1,158,598. Patented Nov. 2, 1915.

2 SHEETSSHEET 1.

' INVENTOR WW/ RY WAC/M ATTORNEY M. WALKER. COMMUT'ATING DEVICE FORDYNAMO ELECTRIC MACHINES,

APPLICATION FILED NOV. 30. I910.

Patented Nov. 2, 1915.

2 SHEETS-SHEET 2.

WITNESSES: 6@Z@6rfz 7 BY (2% SE. 6&4? @1141 UNITED STATES PATENT MILES-iJV'ALIKER, OF HALE, ENGLAND, ASSIGNOR TO WESTINGHOUSE ELECTRIC ANDMANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

GOMMUTATING DEVICE FOR DYNAMO-ELECTRIC MACHINES.

Application filed November 30, 1910.

To all whom it may concern:

Be it known that I, MlLns WALKER, a subject of the King of GreatBritain, and a resident oi Hale, in the county of Chester, England, haveinvented a new and useful Improvement in Commutating Devices forDynamo-Electric Machines, of which the following is a specification.

My invention relates to dynamo electric machines of .the commutatortype, such, for instance, as direct current generators and rotaryconverters, and it has for its object to provide machines of thischaracter with improved arrangements whereby, among other advantages,satisfactory commutation ofthe armature current may be effectedthroughout a wide rangeof load.

In dynamo electric machines of the kind to which the invention relates,it has previously been proposed to obtain the neces sary commutatingelectromotive force by placing auxiliary field poles between the mainpoles and providing them with exciting windings to be traversed by thear-- mature current. .These auxiliary poles, hereurafter referred to ascommutatmg poles, serve to impress a commutating electrometive forceupon the short circuited portions of the armature windings lying underthe commutator brushes which is proportional to the armature current.

According to the present invention, the winding of a commutating pole ofthis kind is provided with a considerably greaternumberof turns thanwould ordinarily be employed and is connected between two commutatorbrushes of the same polarity,

forming parts of a subdivided current-col-= lecting device, which isconnected to the external circuit of the machine.

In the accompanying drawings, Figure l is a diagrammatic view, in endelevation, of a portion of a dynamo electric machine embodying myinvention. Fig. 2 is a view similar to Fig. 1 but illustrating amodification of the manner of connecting the commutator brushes of themachine to the external circuit. Figs. 3 and 4 are diagrammatic viewsillustrating various systems of connecting the exciting windings of thecommutating poles and the commutator brushes to the external circuit, ina machine embodying my invention.

Reierringnow to Fig. 1, the portion of Specification of Letters Patent.

Patented Nov. 2, 1915.,

Serial No. 594,992.

the dynamo electric machine illustrated comprises a'main pole l andcommutating poles 2, 3. The armature of the machine is indicated at 4 asprovided with the usual slots 5 for the reception of the armaturewlnding, a single coil of which is indicated at 6 as having itsterminals connected to two segments 7, 8 of the commutator cylinder 9.Other commutator cylinder segments are indicated at l0, l1 and 12 andwill be hereinafter referred to, in explaining the operation of themachine. A single collecting device is shown in the figure as comprisingtwo distinct portions or brushes 18, 14 which are located closetogether. The direction of rotation of the armature is indicated by thearrow and the forward brush 13 is connected, in series with the exciting.with a resistance 16, to one end of the exciting winding 15, as shownin the figure. The main pole 1 of the machine is provided with the usualseries field winding 18 and shunt field winding 19.

The operation of the machine will be readily understood from thefollowing explanationz-Assuming that the composite current-collectingdevice 13, 1 1 is positive and is situated in the true neutral axis ofcommutation for no load on the machine, the said axis would, if it werenot for the action of the commutating pole, be shifted i'orward in thedirection of rotation, as the load on the machine increases, with theresult that the potential at the commutator segments 7, 10 and 12 wouldbe higher than i the potential at the commutator segments 8 and 11.

There is thus a tendency for a greater portion of the current collectedfrom the armature winding to traverse the brush 13 than the brush 1%,the self-induction. of the coil 6, which is, for the moment, undercommutation, serving to assist this tendency. As is well known, theprovision of the commutating pole 3 will tend to make the potentialat-the commutator segments 8 and 11 greater than the potential at thecommutator segments 7, 10 and 12, this ac tion serving to cause areversal in the direction of the current traversing the coil 8, which isunder commutation. so as to prement 12 leaves the brush vent sparkingwhen the commutator seg- 13. The flux through the commutating pole,hereinafter referred to as the commutating flux, must, in machines asusually constructed, vary in strict accordance with the load, in orderto secure satisfactory commutation.

In a machine constructed according to the present invention, anadjustment of the com-- mutating'flux is automatically obtained by theaction of thebrushes 13, 14 and the exciting winding 15 ot' thecommutating pole above described.

The number of turns of the exciting winding 15 is so selected that, whenthe said winding is traversed by one half of the current traversing thecomposite collecting device 13, 14, the magneto-motive force due to thecorresponding ampere turns will cause such a flux through thecommutating pole 3 that satisfactory commutation is effected, theself-induction of the coil 6, under co1nmutation, being neutralized soas to obtain an equal division of the current between the brushes 13,14. These conditions being obtained for any one load, the apparatus willbe found' to be automatically self-adjusted throughout a Wide range ofload, since, if the commutating pole is too strong, it increases thecurrent col lectcd by the brush '14, whereas. if the said pole is tooweak, the

r current collected by the brush 13 is 111-- creased. If, for instance,the load on the machine increases to such an extent that the iron on thecommuthting pole 3 begins to be magnetically saturated and therefore torequire an increase'in the current traversing its excitingv windingwhich is proportionately greater than the increase in the load, thecurrent traversing the brush 13 will be increased. The currenttraversing the exciting winding 15, which is connected to the said brush13, will therefore be more than one-half of the total current collectedfrom the composite collecting device and the commutating pole will. beexcited to an extent which is proportionately greater than the increasein the load, so that the conditions of good commutation areautomatically restored.

If the load on the machine increases so suddenly that the commutatingpole 3 cannot respondto the increased exciting current, there is atendency to impose the whole current upon the brush 13 and, when'thisoccurs, all the current will traverse the exciting winding 15 and themagneto-motive force on the commutating pole 3, which is caused thereby,will then be twice as great as is usually the case in commutating polemachines of ordinary type. The above mentioned condition represents theupper limit of the range of automatic adjustment of the commutation ofthe machine and the latter will only fa l to commutate satisfactorilywhen the load is such as to require more than double the number of turnson the commutating pole.

Aswill be readily understood, the present invention avoids the necessityfor very exact adjustment of the ampere turns on the comniutating polein order to insure satisfactory commutation, since, if the said ampereturns are not of the proper value for good commutation at any load, thecommutating 3, or, in some cases, the said resistance may be madeconsiderably smaller than that of the coil 15, or even omittedaltogether, and, in such cases, it is preterableto slightly reduce thenumber of turns in the exciting coil 15 by such an amount that theelectrolnotive force at the commutator segments 7, 10 and 12 under thebrush 13 is sutiicientl y greater than the electromotive force at thecommutator segments under the brush 11 to overcome the drop in voltagethrough the exciting coil 15.

Referring now to Fig. 2 a modification of the arrangement of Fig. 1 isshown in which the conductor 17 is connected to an intermediate point inthe winding 15, the effect of such connection being to insert avorrespending resistance in the circuit leading from the brush 1% and,at the same time,

since the current traversing the said brush passes through a portion oithe exciting winding 15 in a reverse direction to that of the currenttraversing the brush 13, an excessive current traversing the brush 14will havethe effect of (lo-magnetizing, or even reversing, the polarityof the commutating pole 3.

The portions of the machine illustrated in Figs. land 2 show only asingle positive current-collecting device. The negativecurrent-collecting devices are not shown in these figures, but may besubdivided in a similar manner to the collecting device 13, ll or eachof these may consist of a simple brush, In the latter case, thedistribution of the current over the contact surface of the brush willbe rendered suiiicientlyuniform by the action of the positive brusheswhich automatically maintain the commutating tiux at' will be seen fromthe figure, all the forward brushes 13 are connected to a commonconductor 22, which is connected, through the exciting coils 15 of allthe commutating poles, in series with one another, to one terminal 17 ofthe external circuit of the machine. All the backward brushes 14 aresimilarly connected to a common conductor which is connected througharesistance 16 to the terminal 17 connected together to theoppositeterminal 20. The connection system shown in Fig. 3 may evidently bemodified by'connecting the exciting windings 15 of the commutating polesin. parallel with one another instead of in series, as shown in Fig. 3,in which case the connection of each exciting winding 15 to itscorresponding brushes 13, 14 may be separate and distinct from theconnections of the remaining commutating poles and brushes, as shown inFigs. 1 and It will be obvious thatyin the connection system of Fig. 3,the brushes 13, 14 may be the negative current-collecting device and thesimple brushes 21 the positive collecting devices provided that theconnections of the exciting windings 15 are so arranged that the properpolarity is given to the commutating poles. It is also possible toemploy both positive and negative subdivided current-collecting devices,such an arrangement being shown in Fig. 4. Each of the exciting windingsof the commutating poles is in this case divided into two parts 25 and26. The conductors 22 and 23 connected to the positive brushes 13, 14are in this case connected to the terminal 1'1 in series with theexciting windings 25 and the resistance 16, respectively. The subdividednegative brushes 2? and 28 are similarly connected to common conductors29 and 30, respectively, the con ductors 29 and 30 being connected tothe other terminal 20 in series with the exciting windings 26 and aresistance 31, respectively. Other systems of series or parallel connection of the exciting windings of the commutatin poles may obviously beemployed.

From the foregoing description it will be readily understood that a moreor less uniform distribution of the current through the different partsof the collecting devices or brushes is obtained by the use of theinvention and it is therefore possible to use brushes of considerablygreater Width than those ordinarily employed, thereby efiecting areduction in the size of the commutator required for a given current.

I claimns my invention:

1. In a dynamo-electric machine wherein the commutating axis shifts withchanges of load, the combination with a connnutating pole excitingwinding divided into two unequal parts, of a main current brush dividedinto two circumferentially separated parts, connections whereby thebrush part in the The negative brushes 21 are all being connected todirection of heavy load shift of the commutating axis supplies currentto an external circuit through the major portion of saidexcitingwinding, the magnetic fields thus produced in the two portions oftheexciting winding opposing each other.

2. A dynamo electric machine having commutating poles provided withexciting windings connected in the external circuit and commutatorbrushes severally di- -vided into a plurality of parts that areinsulated from one another, the said parts different points in thecommutating pole windings, whereby the relation between the currentstraversing the several parts of'such collecting devices is controlled bycausing any excessive current traversing one of the said part to varythe excitation of the corresponding COITIIIIU- tating pole and therebychange the fiux of the said pole to restore the normal current relationbetween the said parts, substantially as described.

3. A dynamo electric machine of the commutator type comprising a fieldmagnet having main and commutating poles provided with excitingwindings, and two adjacent main brush parts of the same polarity thatare insulatedfrom each other and are connected to the external circuitthrough unequal portions of the exciting windings of the commutatingpoles, for the purpose specified.

a. A dynamo-electric machine of the commutator type comprising main andcommutating field magnet poles, commutating field windings on the saidcomn'iutating poles, a resistor, and two adjacent main brush parts ofthe same polarity that are insulated from each other and arerespectively connected to the external circuit through the saidcoinmutating windings, and through the said resistor, whereby thecurrents traversing the two brush parts produce opposing magnetizations.substantially as and for the purpose specified.

A dynamo-electric machine of the 001m mutator type comprising a two-partmain commutator brush, a commutating pole provided with a winding havinga considerably larger number of turns than would normally be required tocommutate the full-load current of the machine, connections from the twoparts of the said commutator brush to different points on the saidwinding. and a lead adapted to connect the said winding to an externalelectric circuit.

6. A dynamo electric machine of the. commutatortvpe having commutatingpoles provided with exciting windings, a plurality of main brushes thatare severally divided into two parts for connection to difierent partsof subscribed my name this tenth day of N0 the exciting windings of thecommutating vernber 1910.

poles of the machine, and a connection from 7 MILES xWALKER stillanother part of the exciting Winding to 5 an external circuit,substantially as de Witnesses:

scribed. F. Ln FALL,

In testimony whereof, I have hereunto I A. b. OACHEMAILLE.

